Light detectors are well known and involve a light sensitive element, such as a photocell, which is actuated by a light source. Light detectors are used in a great variety of applications including shaft encoders in which an optically coded disc is moved over an array of photo detectors whose outputs define the relative position of the coded disc. Paraboloid (three dimensional) light reflectors are well known for focusing of light such as produced in flashlights.
In a common arrangement for an array of photocells, a plurality of light sources are used, one for each photocell in the array. In certain applications, however, such multiple light sources are impractical for reasons of economy, space or reliability. A longitudinal light source such as a flourescent light could be used for illuminating an array of photocells, but such light source is not conveniently employed in a cost effective application.
In certain products such as consumer wares, the product's safety, cost effectiveness, convenience of installation, reliability and efficiency often can make the difference between a successful and unsuccessful product. For example, in the production of a digital bathroom scale for use in the home, it is important that the scale is safe and convenient to use. Electrical power is needed to drive the scale's shaft encoder and when this power is derived from a conventional AC outlet, additional components to provide a safe product increase the product expense, especially when the high voltage is run directly into circuits inside the scale. Even the use of an AC to low voltage DC socket mounted converter, as are commonly used to drive small appliances, though safe to use, increases scale cost, and requires scale attachment to a wire which some customers are likely to find impractical.
Use of a battery driven shaft encoder, however, imposes difficulties such as a need to minimize power utilization to conserve the batteries and stretch out time intervals between battery changes. Such low power drain must be compromised with the need to provide a satisfactory light intensity needed to actuate photocells as may be employed in the shaft encoder. Use of a plurality of light sources to actuate the photocells can be used, but these tend, on the aggregate, to impose a higher electrical power drain and with the need of appropriate components and mountings with lamps or light emitting diodes, additional costs.